AP Exam 2

What is blood flow

The volume of blood flowing through a vessel or organ. Normally equal to Cardiac Output

What is blood pressure

Is the force per unit area that blood exerts on a vessel.

Systolic - when the ventricles contract (120mmHg)
Diastolic - when the heart relaxes - (80mmHg)

What is resistance

opposes blood flow in a vessel. Resistance increases as you get further from the heart.

• Diameter has the most impact on resistance

caused by vasoconstriction and vasodilation mainly of arteries.

What happens to flow if resistance increases or decreases?

• If Resistance goes down then blood flow increases.

• If Resistance goes up then blood flow decreases.

• Resistance is the most important effector of flow because vessels can dilate or constrict.

Factors that can impact flow and pressure.

• Blood Viscosity

• Blood Vessel length

• Blood vessel diameter

Know the mechanism behind capillary exchange.
▪ What pushes fluid out?
▪ What pulls it back in?
▪ What happens if blood pressure is too high/low at the arterial end?
▪ How is capillary exchange related to edema?

• What pushes fluid out?

  • Hydrostatic pressure (blood pressure) at the arterial end of the capillary.

• What pulls it back in?

  • Osmotic (oncotic) pressure from plasma proteins, mainly albumin, at the venous end.

• What happens if blood pressure is too high/low at the arterial end?

  • Too high: More fluid is pushed out than can be reabsorbed, leading to potential edema.

  • Too low: Less fluid is pushed out, reducing nutrient and oxygen delivery to tissues.

• How is capillary exchange related to edema?

  • If hydrostatic pressure is too high, osmotic pressure is too low, or capillaries become too permeable, excess fluid remains in tissues, causing swelling (edema).

Know how veins return blood to the heart.

1.Structural Modifications: Large lumens and valves to prevent back flow.
2. Respiratory pump – Abdominal pressure increases during breathing and
squeezes veins, forcing blood upward through valves toward heart.
3. Muscular Pump – As skeletal contract and expand they squeeze surrounding
veins and “milk” the blood up through the valves.
4. Above the heart, gravity plays an important role in venous return.

Regulation of blood pressure and flow
▪ metabolic needs
▪ nervous regulators
▪ chemical regulators
▪ baroreceptors

Metabolic Needs

• Tissues regulate their own blood flow based on oxygen and nutrient demands.

• Vasodilation occurs when tissues have low oxygen or high CO₂, H⁺, or lactic acid (e.g., during exercise).

• Vasoconstriction occurs when metabolic demand is low.

Nervous Regulators

• The autonomic nervous system (ANS) controls blood vessel diameter.

• Sympathetic stimulation increases heart rate, cardiac output, and vasoconstriction, raising blood pressure.

• Parasympathetic stimulation (via the vagus nerve) lowers heart rate, decreasing blood pressure.

Chemical Regulators

-Adrenal Medulla hormones – increase BP.
▪ Angiotensin II – increases BP, part of the renin-angiotensin-aldosterone
mechanism
▪ ADH – increases water retention and increases BP.
▪ ANH – increases water loss and decreases BP.
▪ NO – major vasodilator – mainly in vessels leading to genitalia

Baroreceptors

• Found in the carotid sinuses and aortic arch, these receptors detect blood pressure changes.

• If BP rises/increased stretch, baroreceptors send signals to the brainstem, triggering vasodilation and a lower heart rate.

• If BP drops/decreased stretch, they signal for vasoconstriction and increased heart rate to restore BP.